It is important to know exact operating baud rates to achieve successful asynchronous serial digital communication. Practically, however, it is not possible to know the baud rate of each transmitter. Therefore, to obtain effective communication, receivers are typically provided with baud rate detectors.
In general baud rates are detected by measuring the time period of either the start bit or the complete data frame. Extensive work has been carried out for automatic detection of baud rates during communication. However, this work has been aimed at providing a dedicated hardware solution rather than an on-chip or integrated solution.
U.S. Pat. No. 3,747,074 describes an exemplary baud rate detector. In the described detector, additional hardware is provided with integrated circuits to detect the communication baud rate. To determine the baud rate, a predetermined frame of data is transmitted through the transmitter. Time for each transition is recorded and an average of the total time taken and bits transmitted are used to determine the baud rate.
U.S. Pat. No. 5,490,209 describes another baud rate detector that operates to determine the highest operating baud rate. A highest possible baud rate is selected and then, a predetermined set of data frames is received from a transmitter. Further, the patent describes a communication method in which the baud rate is lowered in small steps until the data frames are received undistorted. U.S. Pat. No. 6,366,610 describes yet another baud rate detector that also utilizes additional hardware to determine baud rates.
There remains a need for an on-chip technique for detecting baud rate with accuracy.